Tumors are dependent upon new blood vessel formation, or angiogenesis, for expansive growth. We have recently developed techniques that have enabled us to isolate endothelial cells that line blood vessels from normal resting livers and regenerating livers in mice. We have previously unraveled gene expression profiles in endothelial cells 6 hours following partial hepatectomy. Data from our previous work in this area have indicated that some genes can be turned on very rapidly following an angiogenic stimulus. However, a comprehensive analysis of which genes are turned on early has not yet been performed. The rational for this project is that early response genes are more likely to be involved in driving the angiogenic process. Identification of early regulatory genes could lead to new vascular targets that could ultimately be used to manipulate angiogenesis-dependent diseases such as cancer.